﻿Either both parameter, <em>ThresholdDepth</em> and <em>ThresholdThickness</em> are given, or only the <em>ThresholdThickness</em>, then the <em>ThresholdDepth</em> is variable. It is not valid to only assert the <em>ThresholdDepth</em>.
<blockquote class="note">NOTE&nbsp; A <em>ThresholdDepth</em> with NIL ($) value indicates a door style with a lining equal to the wall thickness.</blockquote>
<blockquote class="change-ifc2x4">IFC4 CHANGE&nbsp; Rule corrected.</blockquote>